This invention relates to a blanking pulse generator useful in conjunction with television kinescope deflection circuits having inherent delay.
A switched synchronuus vertical deflection (SSVD) circuit is described in U.S. Pat. No. 4,048,544 issued Sept. 13, 1977 to Peter Eduard Haferl and entitled "SWITCHED VERTICAL DEFLECTION SYSTEM" in which energy is supplied to the vertical deflection winding on a kinescope by means of switched reactances coupled to the horizontal deflection generator. The switched reactances are controlled by a vertical sawtooth generator, the trace and retrace intervals of which are in turn controlled by the vertical synchronizing signals. A pulse position modulator driven by the sawtooth generator and synchronized with the horizontal retrace pulses generates switch gating signals which control the switched reactances in a manner to generate a sawtooth deflection current at the vertical rate in the vertical deflection winding. This arrangement has a low power consumption by comparison with other vertical deflection circuits and is considered commercially advantageous.
As is well known, it is very advantageous from the point of view of cost and reliability to include as many of the functions of a television receiver as possible within integrated circuits. Similarly, for standardization purposes it is highly desirable to produce integrated circuits in a fashion such that they are adapted for use with a wide variety of television receivers.
Since the low-power portions of a television receiver including a synchronous switched vertical deflection circuit according to the aforementioned U.S. Pat. No. 4,048,544 are relatively complex, an advantage in cost and reliability, as well as in serviceability, may be obtained by forming the pulse position modulator on an integrated circuit together with other ancillary circuits such as a blanking pulse generator. It has been discovered, however, that a switched synchronous vertical deflection system according to the aforementioned U.S. Pat. No. 4,048,544 has an inherent delay between the generated vertical sawtooth and the resulting vertical deflection current which depends upon the design of the deflection winding, which in turn depends upon the kinescope size and type. The magnitude of this delay has been observed to be in the range between 30 and 150 microseconds, and in special cases almost zero. The variation of the delay from receiver to receiver within each type, however, remains relatively constant. Consequently, in order to make it possible for a single control circuit to be used for a large variety of television yoke designs or kinescope sizes, means must be provided for delaying the generation of the transition defining initiation of the blanking pulse relative to the synchronizing pulse. The delay must be by an amount depending upon the delay of the vertical deflection circuit.
It is known from U.S. Pat. No. 3,931,545 issued on Jan. 6, 1976 to Francis C. Marino to allow the horizontal blanking interval to commence in coincidence with a horizontal synchronizing pulse but to delay the cutoff of the horizontal output transistor by a period of time equal to the entire horizontal sweep period less the transistor storage time by the use of multivibrators in tandem. This, however, is vulnerable to display distortion due to sweep jitter resulting from the regenerative nature of the multivibrators.
Furthermore, it is desirable to control the duration of the kinescope blanking pulse generated within the receiver so that portions of the vertical blanking interval not used for vertical retrace may be used for facsimile reproduction or other information transmission. However, as is well-known, the incorporation of large numbers of functions into integrated circuits places a premium upon the number of interface connections or terminals between the inside and outside of the integrated circuit. Thus, it is desirable to control both the delay occurring before initiation of the blanking pulse and its duration from a single interface terminal assigned exclusively for this purpose.